Milecastle 17 (Welton/Whittledean) was a milecastle of the Roman Hadrian's Wall. The milecastle is located near to the Whittle Dene reservoirs and is visible as a platform in the ground. Just 174m west of the milecastle is a distinct change in wall construction, indicating that it may have formed a boundary between different legions. The existence of the milecastle has been known since at least 1732 and excavations have produced numerous finds and evidence of post-Roman occupation. The associated turrets both lie beneath the B3618 Military Road. A stone found near the milecastle is the only known written record of the name of Gaius Julius Marcus, a Roman Governor of Britain whose name has been erased from other inscriptions possibly because he fell out of favour with Emperor Caracalla. Construction Milecastle 17 was a short-axis milecastle with Type I gateways. Short axis milecastles are thought to have been constructed by the Legio II Augusta who were based in Isca Augusta (Caerleon). The milecastle is located near to Welton, Northumberland and around from the Whittle Dene reservoirs from which it derives its common names. The remains of the milecastle are visible in the ground as a low platform 14.93m by 17.68m in size. Ploughing has reduced the size of the platform but it remains visible with a scarp on the eastern side and a scatter of stones to mark its position. At a point on the wall 174m west of Milecastle 17 there is a significant change in construction, discovered in 1931. East of this point the wall is constructed at the thickness of the foundations for one course of stone before stepping in to a narrower wall, west of here the wall continues at full foundation thickness for three or four courses before stepping in. In addition the western part tends to use smaller stones, and east of Milecastle 17 until Turret 12A all turrets have east doors and thick walls, with those west until Turret 21A having doors in the western part of the south wall and thinner walls. These differences has been attributed to a boundary between two legions engaged in construction of the wall. A milestone used to stand to the east of the milecastle, erected in AD 213. This stone is now missing but amounts to the only written record of the name of Gaius Julius Marcus, a governor of Roman Britain. During this year it